<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .parent {
            position: relative;
            z-index: 1;
        }

        .parent div {
            width: 100px;
            height: 100px;
            background: red;
            position: relative;
            z-index: 3;
        }

        .box {
            width: 200px;
            height: 200px;
            background: green;
            position: relative;
            z-index: 2;
            margin-top: -10px;
        }
    </style>
</head>
<body>
<!--
    父级是同一个的级别，z-index才可以比较。不同父级的直接比较父级的层级；
-->
<div class="parent">
    <div>lang</div>
</div>
<div class="box">lang2</div>
</body>
</html>